The forming of can ends or shells for can bodies, namely aluminum or steel cans, is well-known in the art. Shells typically have a central panel connected to an inner panel wall which is connected to a countersink. The countersink is usually connected to a chuck wall of the shell which is connected to a peripheral curl that is structured to be seamed onto a can body.
A representative patent disclosing shell forming is Bulso U.S. Pat. No. 4,716,755. As is typically seen, the inner pressure sleeve of a shell press is mounted around a punch core. See, e.g., element 13 of FIG. 1 in Bulso U.S. Pat. No. 4,716,755. Alternatively, the inner pressure sleeve is supported on a column of gas (See, e.g., element 40 of FIG. 2 in McClung U.S. Pat. No. 6,658,911) or the inner pressure sleeve is supported on a piston. These approaches are not without certain limitations though.
The inner pressure sleeve mounted around a punch core, supported on a column of gas or supported on a piston can lead to the inner pressure sleeve heating up excessively in the shell forming process due to the loads that are applied to the inner pressure sleeve from formation of the chuck wall area of the shell being formed. Excess heat generation in the inner pressure sleeve is not desirable in shell forming since the inner pressure sleeve can undergo thermal expansion and cause the press to form shells that do not meet the tolerances required by a can maker.
Also, the inner pressure sleeve mounted around a punch core, supported on a column of gas or supported on a piston can cause excessive strain hardening to occur in the chuck wall area of the shell being formed. Excess strain hardening of the chuck wall is not desirable in shell forming since the final converted can end could crack or deform once the can end is seamed onto a can body containing product that is under pressure.
Due to the potentially high internal pressures generated by carbonated beverages, both the can body and the can end are typically required to sustain internal pressures of 90 psi (0.621 MPa) without cracking or deformation. Depending on various environmental conditions such as heat, over fill, high carbon dioxide content, and vibration, the internal pressure in a beverage may exceed internal pressures of 90 psi (0.621 MPa). Recently, shell developments have been focused on engineering various features of the shell including the chuck wall angle in order to reduce the metal content in the shell and allow the shell to sustain internal pressures exceeding 90 psi (0.621 MPa). Steering away from excess strain hardening of the chuck wall is desirable to avoid catastrophic and permanent deformation of the converted can end.
Another representative patent disclosing shell forming is Hubball U.S. Pat. No. 6,968,724. Huball uses a die core and a punch core with the die core having an outer diameter less than the outer diameter of the punch core. This approach is not without certain limitations though.
The portion adjacent to a surface of the die core in Hubball is not in contact with the die core ring located proximate to the die core. Hubball's approach does not provide the portion adjacent to the surface of the die core with the control, precision and stability one would obtain by having the portion adjacent to the surface of the die core in contact with the die core ring located around the die core.
A need exists in the art for an apparatus and method for forming shells that avoids excessive heat generation in the inner pressure sleeve and selectively biases and controls movement of the inner pressure sleeve to avoid excessive strain hardening of the chuck wall of the shell being formed.
A need also exists in the art for an apparatus and method for forming shells that has a die core with an outer diameter equal to or greater than the outer diameter of the punch core with the portion adjacent to the surface of the die core in contact with the die core ring to provide the die core with greater control, precision and stability.